Dave - I've been looking for the same information too, but so far haven't heard any success stories, so it's on hold. I have an Elk-150RT siren that I would like to use as an alarm, but I am hesitant to try to activate it with the modified Power Horn relay. I even bought some of the parts for a potential relay modification, but chickened out on the following mod.
MSUN2000 on July10, 2006 on the Forum:
"I also found another document to modify the PH508 as relay using different components but sorry I couldn't remember where I got it from (google), but anyway here it is:
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ALTERNATE VERSION:
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One of the great shortcomings of the X-10 wireless security system is the lack of an interface to external devices, like a strobe and/or siren, to alert neighbors of a burglary or other emergency situation. The following modification adds that capability.
When an alarm is activated, the base (receiving) unit wails its siren and sends out alternately, at about one second intervals, the signals ALL LIGHTS ON, ALL UNITS OFF. This has the effect of flashing all lights on the same house code. You can buy a remote, plug-in power siren which has been designed to trigger when it receives 4-5 on-off cycles, alternating its two-tone horn in synch with the ON-OFF signals. However, it is not suitable for outdoor installation.
As noted by others, the power siren circuit board contains space for an optional external relay interface circuit, although units with this option seem never to have been produced. It would provide a low-voltage contact closure (30VAC, 2A max.).
In this note I will describe how to make the modification, based on schematics from X-10 engineering and my own testing. This improves upon earlier recommendations in the X-10 FAQ.
Modification:
Install the following components in their marked location on the circuit board:
R30 470 ohm 2 watts do not allow to touch other components
R31 2.7 K 1/2 watt just fits: do not substitute or leave out
R32 2.7 K 1/4 watt
R33 100 K 1/4 watt
R34 100 K 1/4 watt
R35 150 K 1/4 watt
R36 1 K 1/4 watt
C18 10 uf 16 volts + on board is marked with a diamond
D16 1N4001 1 AMP diode
TR8 TEC9014 (almost any 100ma NPN switching transistor will work)
RL1 5 volt, 72 ma DIP relay, Radio Shack #275-243
Remove R8 (or just clip the leads). There may be a resistor in parallel with R8, remove it also. This was used to keep the unregulated and unloaded + supply from floating up too high, and is now taken care of by R31.
Activated (and unmodified), the unit consumes about 70ma, powered on the - side by a 100ma regulator. The relay modification consumes an additional 70 ma, over-taxing the power supply and regulator. Even though it will still work for a brief time when activated, you risk having the regulator shut-down or the transformer overheat. To get reliable operation within safe-area limits, change the wiring to the piezo elements. The unit comes from the factory in which all four elements are wired in parallel. Change the wiring so that they are in a series-parallel configuration, reducing their current drain from 50ma to 12.5ma, and reducing their total sound level from 105db to 99db.
Code:
--| |-- --| |--
__/ \__/ \__ (piezo element wiring change)
\ / \ /
--| |-- --| |--
You should maintain consistent polarity when rewiring the elements, and if you are clever, you can do it by removing one brown wire at the top, switch the polarity of the other brown wire at the top, and use the wire you removed to relocate and extend the blue wire to the opposite side (cover the exposed connection). Since you are going to hook up an external siren presumably, the loss of indoor volume should not pose a problem (I think it's too loud anyway).
Finally, you need to install screw terminals in the slots provided. I used terminals taken from an X-10 door/window sensor in which I permanently soldered the wires connecting to the magnet. Before installing them, you must break off the side tabs which are on top and next to the screw, otherwise the rear cover of the case won't fit. They don't quite stick up as high as I'd like, so if anyone has a better source of screw terminals I'd like to know. Now, remove the adhesive cover plate on the rear cover, and write in red marker next to the terminals "30 volts, 2 amp max."
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So from the docs it looks like a safer mod but it'd be interesting if someone can verify this"
